Flotation of precious metal ores



Feb. 28, 1939. K, KREBS FLOTATION OF RECIUS METAL GRES Filed Feb. 27, 1937 n* :Patented Feb. 28, 1939 PATENT OFFICE AFIiOTATION F PRECIOUS METAL ORES Kellogg Krebs, Monrovia, Calif., assigner to American Cyanamid Company, New York, N. Y., a corporation of Maine- Application February 27, 1937, Serial No. 128,095

2 Claims.

This invention relates to a method of, flotation and particularly to a method of flotation of ores containing precious metals.

, In the past, it has been common practice to interpose a unit notation cell in the grinding circuit :of oreA notation plants, particularly those dealing with precious metal ores. In'such plants there is normally a closed grinding circuit including a mill from which the ground material, after rsuitable conditioning, is introduced into a unit vflotation cell from which a concentrate is scalped .i 'off and the vtailings passed into a classifier from which are scalped of! in the unit cell is often more-than ovset by the-disruptionl of classification conditions, lack of vbalance oi reagents in .the circuit ,and in many cases excessive reagent `uconsumption It will be apparent that the unit cell as used in the past has been a rougher used only for scalping oif a certain proportionof values. I have foundthat'greatly improved recovery, without any of the disadvantages incident to unit cell operation in the grinding circuit, may be obtained if the unit cell is used primarily as a cleaner instead of as a rougher. 'I'his is effected by returning all of the concentrate from the flotation plant to the unit cell feed, the only final concentrate from the whole system being taken off from the unit cell. Under such conditions, the flotation time in theilotation plant proper which now becomes a pure middling circuit, is increased without adversely aecting total capacity; increased pulp density may be obtained without affecting the solids in the classifier underflow, reduced reagent consumption and improved metallurgy. 'Ihe reasons for this surprispassing through the unit cell, may drop in the4 classifier, and the fact that the large unit cell and advantageous pulp density produces an ideal froth Y condition.

In referring to a unit cell in the above gen-A eral description of the invention, it should be 55 understood that this term is 'not necessarily limited to a single iiotation cell. On the contrary,Y a string of flotation cells may be present in the grinding circuit. The advantages of the present invention are, of course, obtained regardless of whether the flotation capacity in the closed 5 grinding circuit is in the form of a single cell or a string of cells.

The present invention is notconcerned with any particular type of reagent and it is an advantage of the invention that it is applicable to 10 the standard reagent combinations. Similarly, the invention may be used with various types of flotation equipment. I'have found that Fagergren mechanical flotation machines are highly effective, particularly in the middlings'circuit 15 and I prefer to use this type of machine, although the invention operates 4with improved results with any type of flotation machine. Itis not so essential to use a Fagergren flotation cell or cells l in the grinding circuit as satisfactory result s can 20 b e obtained with other types of machines in this part of the plant.

The invention is also not broadly concerned with a particular arrangementA of equipment in the` grinder circuit or in the middling circuit.

advantages of the present invention that it is x applicable to existing plants with a minimum of rearrangement and can utilize, for the most part, available equipment.

'I'he invention will be described in greater detail in conjunction with a typical ow sheet which is used with great success in the Spring Hill mine of Grass Valley, Calif. 'I'he drawing is a diagrammatic flow sheet of the grinding and notation portions of this mill.

In the drawing, the ore feed of the Spring Hill 40 mine, which is a quartz and-mineralized diabase and averages about $10 of gold per ton, enters a suitable grinding mill which may be a ball mill of standard construction. The ground ore, 'if necessary after adjustment to suitable pulp density, e. g. about 27% solids, passes into a unit cell 2, where a concentrate is floated oil and thickened in the tower I. The thickened concentrate may then be cyanided in a standard cyanide plant (not-shown). 'I'he tailings from the unit cell 2 50 pass into a4 classiiier 3 from which the underflow is returned to' thegrinding mill. 4'I'he'classiiler overflow runs to a reagent conditioner 6 where it is mixed with approximately .02 lb. of mixture of sodiumdiethyl and' disecondaryJ butyldithio- 55 phosphates, 0.15 lb. per ton" of secondary butylf xanthate, 0.015l ton of cresylic acid, and V2 gallon per ton of 4% stable solution. From the conditioner the yconditioned pulp passes into a string of Fagergren notation cells 5. The tailings are discharged to waste and the concentrate from all ve cells returned to the unit cell feed.

Prior to the use of the present invention, the Spring Hill plant was operated in the normal Heads Tails Conc.

oz. Au oz. Au oz. Au

october 0.18 0.025 i 10.191 November 0. 17 0. 018 10. 95 December 0.12 0.019 9.08

During the months of October, November and December (over the line) the plant operated in the ordinary manner. Beginning with January. the flow sheet of the present invention went into operation.

While marked improvement is shown by the present invention in all of the months showing both lower tails and richer concentrates. the improvements aremore striking in the months when the plant operated on richer feed, namely, 0ctober, as contrasted with January. In the Spring Hill plant it was desired to obtain low tails and high grade concentrates, rather than to effect a maximum economy in reagents. Therefore, the amount of reagents was not decreased. With lower grade' ores where the reagent cost is proportionately a larger item, a better co'mpromise is frequently obtainable by lowering the reagent consumption and keeping recovery constant, or by lowering the reagent consumption somewhat and obtaining improved metallurgy. Every plant presents an individual problem and the best compromise between reagent saving and metallurgy will have to be chosen for each plant. It is an advantage of the present invention that it is very flexible and permits obtaining the most 20 economical compromise in each particular case.

I claim:

1. A method of recovering values from the ore by notation which comprises gnnding ore, floating the ground ore, classifying otation tailings, returning oversize to the grinding plant, oating undersize to form a concentrate and tailing, discarding this second tailing and returning the concentrate to the feed of the otation unit in the grinding circuit.

2. A method according to claim 1 in which the undersize of the classier is conditioned with flotation reagents between the classifier and the second notation plant.

KEILOGGKREBS. 

